Two Class-D personnel, equipped with one (1) Type V Ultraviolet Blacklight. Subjects diminished SCP-P's size, but SCP-P managed to manifest using the UV rays, killing both personnel and breaching containment, resulting in the death of ██ personnel.

This is good, because it tackles a problem well. The Foundation understands that they have to try different spectra of light to invoke a reaction.

Your grammar and spelling are generally excellent and it looks like you thought this out a lot.

Your formatting is off: Special containment procedures should be bolded.

Procedures: SCP-P is to be contained in a Class-H Plutonium Alloy airtight, electromagnetically sealed chamber

An alloy is a mixture of metals or a mixture of a metal and another element. You don't list a second ingredient. More importantly: Unless there's a good reason for your SCP to be contained in your specifications to the letter, you might want to trim them down. All it does is distract from your SCP if it's too detailed. Here's an example:

Containment cell must also include twelve square meters (3m * 4m) of Type B Vacuum containers, destroying all means of light from entering SCP-P's containment cell. SCP-P's containment cell, at all times, MUST be at a level of light below 0.000000000173 lux.

OR, we turn the lights off and tell the Containment Specialist not to bring light into the room.

Monitoring must be constant, as SCP-P has been known to absorb light from outside of the container, though the distance of which it can absorb said light is still unknown.

If the reason for your alloy is to block all forms of light, it's not working because it absorbs light from outside of the chamber. If that's the case, is the material of the cell that important?

Why every 63 minutes? Does something horrible happen if they wait 64 minutes instead?
Try to look at it this way (this is a quote from Doing The Safety Dance, which is an excellent read:

If an object needs to be in a crate, don't define it as an oak crate of two inch wall thickness. Asides from blowing the procedures out of proportion, and being a boring read, this is actually a pathway to an in-universe disaster. Consider it from the perspective of a level-0 security worker. You have to perform maintenance on n-th SCP that day, with a list of containment procedures that's a page long, most of it empty fluff. You have a busy day… you might decide to cut a few corners.. perhaps use a walnut crate when oaken ones aren't available. But then… right. Nothing will happen, because the entry had nothing to do with what is necessary for containment. So, next day, you to do it again, because meeting all the asinine requirements is such a chore, right? Right, except the one time you use a martensitic rather than austenitic steel vessel to transport that living ice the eggheads brought from Antarctica. And then carelessly bump it onto the floor. Say hello to containment breach, and goodbye to your legs.

Try to apply this logic to your own Containment Procedures. What is absolutely necessary? What isn't? If something isn't absolutely vital, trim it out.

> IF A DOSE OF AV516 IS MISSED, SCP-P WILL BREACH CONTAINMENT

Capitalizing and bolding text like this is unprofessional. You don't need to draw attention to something in particular; Containment personnel are required to read the procedures in its entirety. More importantly it draws back to a previous point. It looks like you need to draw attention to this. Why? Because the details described before are cluttering the most important aspects of the Containment Procedures.

SCP-P is a figure made purely of light, typically taking shape of a squid-like creature.

Tone's a little bit off here. You might want to try something like: An entity composed exclusively of photons in the [insert frequency here] spectrum, typically assuming a form reminiscent of a Cephalopoda (squid).

which can vary from tentacles to human-shaped arms.

I think you mean arms similar to human arms, not arms shaped like humans.

The appendages can be completely transparent at times but still make physical contact.

Every physicist that reads this will violently spray their coffee over their monitor when they read this. (This might be wrong in the details, I'm not a physicist myself) Photons don't interact that way. The tentacles would be an anomaly of themselves and the Foundation would definitely expand on that.

SCP-P's known method of killing is through serious penetration wounds that are immediately cauterized and burned through by it's appendages, as well as physically melting the victim's body into solid surfaces around it, bending organic matter.

You can take out 'serious'. Apart from being unclinical, if it's a method of killing, we get that the injuries are severe. It's should be its. Bending organic matter? You mean from the body or any organic material that the body happens to touch?

SCP-P shows incredible strength, able to bend or tear any object within it's "vision" SCP-P can not only destroy, but also manipulate the molecular structure of entities around it.

So is this the reason that the alloy is used? Because it wouldn't work then, would it? If it can manipulate molecular structure, it won't matter what material it's contained in. What you COULD do is change this into something that will confuse your SCP. For example (and this is just an idea): Your SCP gets confused if it's contained in reflective surfaces, like mirrors. Cheaper, it works, less headaches for everyone!

Recovered documents from the facility in which SCP-P had originated explain that it is a creature from the fourth or fifth dimension, that was transferred to Earth via [DATA EXPUNGED].

If we're to believe Dr. Michio Kaku, the fourth dimension is time. We're all experiencing the fourth dimension right now.

SCP-P is not known to be completely destructible, and outbreaks of it will occur if it breaches containment.

So it multiplies? Is that what you mean?

SCP-P instances travel between dimensions in specific "Dimension Crystals" (known as SCP-P-1) found in various coordinates of the United States and Mexico.

These would never be called that way by Foundation personnel. If anything, they would be called 'SCP-P-2' or something.

Though it does seem to be indestructible, many attempts to slow down its speed and vitals via firearm or [REDACTED] have been successful in ██% of cases.

Should be in Containment Procedures, uncensored. If I'm a researcher and this thing broke out, I won't know how to slow it down because this is redacted.

Seven Class-D personnel, equipped with one (1) 4" knife blade.

Metrics please.

Subject exposed to SCP-682. Both specimens were able to breach containment together, resulting in the swift destruction of the Heavy Containment Wing of Site-██, as well as the deaths of ██ personnel and injuries of ███ others.

While this isn't a rule, cross-testing with popular SCPs is generally viewed as trying to ride along with them to make yours look better.

One Class-D, introduced into SCP-P's containment cell. The Class-D showed extreme signs of panic and attempted to make his way out of the cell, but was unsuccessful. Surveillance footage revealed that SCP-P proceeded to tear every appendage off of the Class-D while suppressing his esophagus, killing him in ██ seconds.

O..kay? What did we expect to happen?

One researcher, voluntarily introduced to SCP-P. SCP-P came in physical contact with Dr. ████, completely melting his brain and body into the containment cell wall.

Did this researcher happen to be suicidal? They know the risk of an SCP, this makes no sense.

I don't know for sure. I am very hesitant to upload until someone gives me the "OK"

Is it interesting? Is it boring? Is it excessive? Is it to-the-point? Any other feedback and critiques, guys? I'm EXTREMELY hyped to release this SCP if it gets to that point. All feedback is appreciated.

I'm no dimension-ologist, but I don't think dimensions are portrayed correctly here. Can something be from 'the ninth dimension'? Maybe it should be 'from another dimension' or 'an alternate universe'? Not a necessary change, but maybe you should consider it.

Also, how would field agents properly identify a space between dimensions? Maybe, if you want to describe that, you should have the subject describe it in more layman terms? Also, what happened to the mtf? are they presumed dead? did we get them back? I guess the mystery makes it more intense. I definitely think something should be changed in the incident report.

Lastly, I think the scp is interesting, but some people may not view it as scary or terrifying. To change that response maybe consider un-redacting some of the experiments to bring something truly awe inspiring into the 'story'.

very detailed description of what the monster looks like and its "powers" - inevitably these include the ability to kill with ease and escape from containment at will

the practical impossibility of containment is then counteracted with narrative phlebotinum which removes all tension from the story

the monster has no personality

unnecessary "explanation" for the origin of the monster, which either makes no sense or the Foundation has no evidence for it

test logs which reinforce how deadly the monster along the lines of "is it stronger than a machine gun? how about an anti-tank gun?"

This will not survive in anything like its current form. Rather than trying to edit around the edges, you will need to re-think this entirely. You've said above that you want this to be "interesting and cool" - cool is the hardest thing to write, because (almost by definition) trying to be cool makes you not cool.

So let's come at this another way - a discussion around your purpose may help you construct this in a better form. What existing SCPs would you consider "cool"? What makes them cool?

Very well put! I felt like addressing this as well, and probably should have before I dived head-first into the technical issues.

Get away from "type of object" or "sort of creature" and instead start thinking about stories you want to tell. If you want to create a successful monster, the answers to the following questions should be interesting:

Why is this monster here?

What does it want?

How did the Foundation find it?

Why should the reader care about it? (Apart from being dangerous)

As an example, I'd like to take a look at one of my favorite monsters, 096. Here's a thought experiment: Do you think 096 would be half as good without everything surrounding it? The incident reports, the interviews? In one of the incident reports, a hiker triggered 096's response by looking more closely at a photo he took twenty years ago. That means that everywhere in the world, there could be a ticking timebomb that might lead to a massive chain reaction when things go very wrong. The scary hook then isn't what 096 does to you. Instead (for me) it's the unpredictability and the threat of the unknown, loss of control.

Focus on an emotion like that, and make an SCP to evoke that feeling, not the other way around. Trust me, I tried. It's close to impossible.